The present invention relates to an article superior in making waterdrops slip down the surface of the article. This article can be used as a window pane of various vehicles, watercraft and aircraft.
Hitherto, there have been various proposals for increasing water-repellency of an object in order to remove waterdrops from the surface of the object. Japanese Patent Unexamined Publications JP-A-58-122979, JP-A-58-129082, JP-A-58-142958, JP-A-58-147483, JP-A-58-172242, JP-A-58-172244, JP-A-58-172245, JP-A-58-172246, JP-A-58-190840, and JP-A-58-223634 disclose agents that are capable of providing a glass surface with water-repellency. JP-A-58-167448 discloses a low reflectance glass. JP-A-6-16455, JP-A-6-340451, JP-A-7-138046, JP-A-7-138047, JP-A-7-138050, JP-A-7-267684, and JP-A-8-40748 disclose water-repellent glass panes. JP-A-7-9608 and JP-A-4-255343 disclose water-repellent, oil-repellent coating films.
xe2x80x9cThe angle of waterdrop slippagexe2x80x9d can be defined as being an angle of a surface of an article to the level, at which a waterdrop starts slipping down the surface of the article by tilting the article after the deposition of the waterdrop in a predetermined amount on the surface of the article set horizontal. As the angle of waterdrop slippage becomes smaller, the surface of an article becomes superior or easier in making waterdrops slip down the surface of the article.
It is therefore an object of the present invention to provide an article that is small in angle of waterdrop slippage and thereby superior in making small waterdrops slip down the surface of the article.
According to the present invention, there is provided an article superior in slipping a waterdrop down a surface of the article. The article has a substrate; and a functional layer formed on the surface of the substrate. The functional layer is chemically bonded to the surface of the substrate through siloxane-bonding. The article is prepared by a method comprising: (a) preparing a mixed liquid; (b) applying the mixed liquid to the surface of the substrate, thereby to form thereon a precursory layer; and (c) drying the precursory layer into the functional layer. According to a first aspect of the invention, the mixed liquid is prepared by dissolving in a solvent (1) a silicone that is one of a first silicone having at an end a hydrolyzable functional group and a second silicone having at an end a hydrolyzable functional group and at the other end a fluoroalkyl group, (2) an acid, and (3) water. According to a second aspect of the invention, the mixed liquid is prepared by dissolving in a solvent (1) the above silicone, (2) a silica precursor sol, (3) an acid, and (4) water. According to a third aspect of the invention, the mixed liquid is prepared by dissolving in a solvent (1) the above silicone, (2) a fluoroalkylsilane having at its end a hydrolyzable functional group, (3) a silica precursor sol, (4) an acid, and (5) water. Furthermore, an underlayer made from a hydrolyzable silicon compound may be provided between the substrate and the functional layer. In this case, the functional layer is chemically bonded to the surface of the underlayer through siloxane-bonding.
As stated above, the special silicone is used in the invention as an essential component of the mixed liquid. With this, the obtained article becomes unexpectedly superior in making waterdrops slip down the surface of the article. Furthermore, many reaction sites (i.e., the hydrolyzed functional groups) of the silicone are chemically bonded to the surface of a substrate. Thus, the article becomes superior in durability, too.
As stated above, according to the second aspect of the invention, the mixed liquid is prepared by dissolving in a solvent the silicone, a silica precursor sol, an acid, and water. It is preferable that these silicone and silica precursor sol are dissolved at first in a solvent and then these acid and water are added thereto. According to the third aspect of the invention, the mixed liquid is prepared by dissolving in a solvent the silicone, the fluoroalkylsilane (FAS), a silica precursor sol, an acid and water. It is preferable that these silicone, silica precursor sol and fluoroalkylsilane are dissolved at first in a solvent and then these acid and water are added thereto. The silica precursor sol of the second and third aspects of the invention contains a silica precursor. This sol is capable of turning into a gel and then into silica (SiO2) through baking of the gel.
In the invention, it is optional to form between the substrate and the functional layer an underlayer that has at its surface many reaction sites reactive with the silicone of the functional layer. With this, it becomes possible to increase the reaction sites of the silicone that are bonded to the underlayer. Therefore, it becomes possible to further improve the article in making waterdrops slip down the surface of the article. The underlayer may be prepared by a method comprising (a) applying a silicon compound (e.g., tetraisocyanate silane) that is hydrolyzable at a relatively low temperature (e.g., room temperature), to the surface of the substrate, thereby forming thereon a precursory layer; and (b) drying the precursory layer into the underlayer. If, for example, tetraisocyanate silane is applied to a glass substrate, it is hydrolyzed at room temperature by moisture in the air and then dried at a drying temperature into a silica film. This silica film is strongly attached to the glass substrate through siloxane-bonding. The silica film further has at its surface many silanol groups, which are reactive with the silicone and with the hydrolyzable functional groups of the fluoroalkylsilane of the functional layer. The lower the drying temperature for forming the silica film, the greater the number of silanol groups formed on the surface of the silica film. In view of this, it is the most preferable to use tetraisocyanate silane as the coating liquid, because tetraisocyanate silane can be dried into a silica film at room temperature. Alternatively, perhydropolysilazane can be used as the coating liquid.
In the invention, it is necessary to use in the preparation of the article the above special silicone that is one of (1) a first silicone having at its end a hydrolyzable functional group and (2) a second silicone having at its one end a hydrolyzable functional group and at the other end a fluoroalkyl group. A functional layer can be formed on a glass substrate by dissolving the special silicone in an organic solvent (e.g., alcohol) and then by applying the resultant coating liquid to the glass substrate. After this application, the functional end-group of the silicone is hydrolyzed by moisture in the air. With this, the hydrolyzed end-group is chemically bonded to the surface of the glass substrate. Therefore, the obtained functional layer becomes superior in durability. If acid and water are additionally added to the coating liquid, it becomes possible to accelerate the hydrolysis of the functional end-group of the silicone. In particular, in case that the substrate is made of glass, more reaction-sites (i.e., the hydrolyzed functional groups) of the silicone are chemically bonded to the surface of the substrate by the addition of acid and water to the coating liquid. With this, the article becomes superior in durability and also in slipping waterdrops down the surface of the article. The acid content of the coating liquid is preferably from 0.001 to 0.2 wt %. The water content of the coating liquid is preferably from 0.1 to 20 wt %.
If the second silicone, which has at its one end a hydrolyzable functional group and at the other end a fluoroalkyl group, is used as the silicone in the preparation of the mixed liquid, the obtained article may become superior in oil-repellency as well as in slipping waterdrops down the surface of the article. This oil-repellency may also be obtained by using the above-mentioned fluoroalkylsilane according to the third aspect of the invention. The use of too much amount of this fluoroalkylsilane, however, may cause an adverse effect on the article in slipping waterdrops down the surface of the article.
In accordance with the second and third aspects of the invention, a small amount of a silica precursor sol may be added to the special silicone. With this, more reaction-sites of the functional layer are chemically bonded to the surface of the substrate. Thus, it becomes possible to further improve the article in slipping waterdrops down the surface of the article, since the silica precursor sol has many functional groups that are capable of reacting with the substrate""s surface and with the functional groups of the silicone of the functional layer. Thus, this silicone can be bonded directly to the substrate and at the same time can be bonded indirectly thereto through its bonding with the silica precursor sol. Therefore, it becomes possible to increase the number of the reaction sites of the silicone that are bonded to the substrate""s surface. For obtaining this increase, it is optional to combine the addition of a silica precursor sol to the special silicone with the above-described formation of the underlayer.
In the invention, each hydrolyzable, functional end-group of the first and second silicones is not particularly limited as long as it is hydrolyzable and thereby can chemically be bonded to the substrate or the underlayer. Each end-group is preferably at least one group selected from alkoxysilyl groups, hydroxysilyl groups, halogenated silyl groups (e.g., Sixe2x80x94F, Sixe2x80x94Cl, Sixe2x80x94Br, and Sixe2x80x94I), acyloxysilyl groups, and isocyanate silyl groups.
In the invention, it is preferable that the special silicone has a molecular weight of greater than 1,000 in order to improve the article in making waterdrops slip down the surface thereof. If its molecular weight is not greater than 1,000, the article may become inferior in making waterdrops slip down the surface thereof. It is assumed that methyl groups (hydrophobic groups) of the silicone are not oriented in good order at the surface of the functional layer if the molecular weight is not greater than 1,000.
In the invention, the content of the solid matter of the silicone in the mixed liquid is preferably from 0.05 to 20 wt %, particularly from 0.5 to 5 wt %. With this, the article is improved in making waterdrops slip down the surface thereof, and the functional layer becomes sufficiently transparent. If it is less than 0.05 wt %, the number of the reaction sites of the silicone that are bonded to the surface of the substrate or underlayer may become too small. With this, the article may become inferior in making waterdrops slip down the surface thereof. If it is greater than 20 wt %, the silicone may be aggregated after the application of the mixed liquid. With this, the distribution of the reaction sites of the silicone may become uneven. Thus, the article may become inferior in making waterdrops slip down the surface thereof.
According to the second aspect of the invention, the ratio by weight of the solid matter of the silica precursor sol to the solid matter of the silicone is preferably from 0.001 to 0.5, particularly from 0.005 to 0.1. Similarly, according to the third aspect of the invention, the ratio by weight of the solid matter of the silica precursor sol to the total solid matters of the mixed liquid is preferably from 0.001 to 0.5, particularly from 0.005 to 0.1. If it is less than 0.001 in each of the second and third aspects of the invention, it may not be possible to further increase the number of the reaction sites of the silicone that are bonded to the surface of the substrate or underlayer. Thus, the article may not be sufficiently improved in making waterdrops slip down the surface thereof. If the ratio is greater than 0.5 in each of the second and third aspects of the invention, the mixed liquid may have aggregates. Furthermore, the relative amount of the silicone in the mixed liquid is decreased. Therefore, the article may not be sufficiently improved in making waterdrops slip down the surface thereof.
According to the third aspect of the invention, the amount of the fluoroalkylsilane is preferably up to 70 wt %, particularly up to 50 wt %, based on the total weight of the silicone and the fluoroalkylsilane. If it is greater than 70 wt %, the action of the fluoroalkylsilane to attract waterdrops may become too strong. With this, the article may become inferior in making waterdrops slip down the surface thereof.
Preferable examples of the first silicone are CH3xe2x80x94(Si(CH3)2xe2x80x94O)nxe2x80x94Si(CH3)2OCH3, CH3xe2x80x94(Si(CH3)2xe2x80x94O)nxe2x80x94SiCH3(OCH3)2, CH3xe2x80x94(Si(CH3)2xe2x80x94O)nxe2x80x94Si(OCH3)3, CH3xe2x80x94(Si(CH3)2xe2x80x94O)nxe2x80x94Si(OC2H5)3, CH3xe2x80x94(Si(CH32xe2x80x94O)nxe2x80x94Si(CH3)2(CH2)3OCH2CH(OH)CH2NH(CH2)3Si(OCH3)3, CH3xe2x80x94(Si(CH3)2xe2x80x94O)nxe2x80x94Si(CH3)2((CH2)3OCH2CH(OH)CH2)2N(CH2)3Si(OCH3)3, CH3xe2x80x94(Si(CH3)2xe2x80x94O)nxe2x80x94Si(OH)3, CH3xe2x80x94(Si(CH3)2xe2x80x94O)nxe2x80x94Si(CH3)2Cl, CH3xe2x80x94(Si(CH3)2xe2x80x94O)nxe2x80x94Si(CH3)2(CH2)2SiCH3Cl2, CH3xe2x80x94(Si(CH3)2xe2x80x94O)nxe2x80x94SiCl3, CH3xe2x80x94(Si(CH3)2xe2x80x94O)nxe2x80x94Si(OCOCH3)3, CH3xe2x80x94(Si(CH3)2xe2x80x94O)nxe2x80x94Si(NCO)3, and CH3xe2x80x94(Si(CH3)2xe2x80x94O)nxe2x80x94Si(CH3)2(CH2)3O(CH2)3OCONHSi(NCO)3. Preferable examples of the second silicone are Rfxe2x80x94(CH2)2xe2x80x94(Si(CH3)2xe2x80x94O)nxe2x80x94Si(CH3)2(CH2)3OCH2CH(OH)CH2NHSi(OCH3)3, and (Rfxe2x80x94(CH2)2xe2x80x94(Si(CH3)2xe2x80x94O)nxe2x80x94Si(CH3)2(CH2)3OCH2CH(OH)CH2)2N(CH2)3Si(OCH3)3. In each of these preferable examples of the first and second silicones, n is greater than 13. With this, each of these preferable examples has a molecular weight of greater than 1,000. In each of these preferable examples of the second silicone, Rf is a fluoroalkyl group. This fluoroalkyl group of the second silicone may be selected from straight-chain and branched perfluoroalkyl groups each having a carbon atom number of 1-16. Of these, the fluoroalkyl group is preferably C8F17xe2x80x94 in order to provide the functional layer with water-repellency and oil-repellency.
The silica precursor sol, which is used for preparing the mixed liquid, may be selected from commercial products such as SUPERCERA (trade name) of Daihachi Chemical Industry Co., CERAMICA (trade name) of Nichiita Kenkyusho Co., HAS (trade name) of Colcoat Co., ATRON SiN-500 (trade name) of Nippon Soda Co. Ltd., LICKSON COAT CGS-D1-0600 (trade name) of Chisso Co., and COLCOAT P and COLCOAT 6P (trade names) of Nippon Colcoat Co.
The fluoroalkylsilane may be selected from CF3CH2CH2Si(OCH3)3 (TSL8262 (trade name) of Toshiba Silicone Co.), CF3CH2CH2SiCl3 (TSL8261 (trade name) of Toshiba Silicone Co.), CF3(CF2)5CH2CH2SiCl3 (TSL8256 (trade name) of Toshiba Silicone Co.), CF3(CF2)5CH2CH2Si(OCH3)3 (TSL8257 (trade name) of Toshiba Silicone Co.), CF3(CF2)7CH2CH2SiCl3 (TSL8232 (trade name) of Toshiba Silicone Co.), CF3(CF2)7CH2CH2Si(OCH3)3 (TSL8233 (trade name) of Toshiba Silicone Co.), CF3(CF2)7CH2CH2SiCH3Cl2 (TSL8229 (trade name) of Toshiba Silicone Co.), and CF3(CF2)5CH2CH2SiCH3(OCH3)2 (TSL8231 (trade name) of Toshiba Silicone Co.). Fluoroalkyl group of the fluoroalkylsilane may be selected from straight-chain and branched perfluoroalkyl groups each having a carbon atom number of 1-16. Of these, it is preferably a straight-chain fluoroalkyl group represented by C8F17 in order to provide the functional layer with water-repellency and oil-repellency. Functional groups of the fluoroalkylsilane other than fluoroalkyl group are not particularly limited as long as they are hydrolyzable and thereby can chemically be bonded to the substrate or the underlayer. Preferable examples of these functional groups are alkoxysilyl groups, hydroxysilyl groups, halogenated silyl groups (e.g., Sixe2x80x94F, Sixe2x80x94Cl, Sixe2x80x94Br, and Sixe2x80x94I), acyloxysilyl groups, and isocyanate silyl groups.
The solvent, which is used for preparing the mixed liquid, is not particularly limited so long as it dissolves the components of the mixed liquid. It may be selected from primary alcohols (e.g., methanol, ethanol, and propyl alcohol), secondary alcohols (e.g., isopropyl alcohol), tertiary alcohols (e.g., txe2x80x94butanol), ketones (e.g., acetone and methyl ethyl ketone), ethers, and aliphatic, aromatic and alicyclic hydrocarbons (e.g., benzene, toluene, xylene, chloroform, pentane, hexane, and cyclohexane). Of these, a polar solvent can be used alone or mixed with another solvent for dissolving the components of the mixed liquid. In contrast, a non-polar solvent can be mixed with another solvent for that. The acid, which is used for preparing the mixed liquid, is not particularly limited. It may be selected from various organic and inorganic acids.
The manner of applying the mixed liquid to the substrate or the underlayer may be dip coating, spraying, flow coating, spin coating, or roller coating.
As stated above, the special silicone is mixed with acid and water in a solvent. With this, the hydrolyzable, functional end-groups of the silicone are hydrolyzed and thereby activated. This mixing is conducted at a temperature of preferably from room temperature to 70xc2x0 C., particularly from 30 to 50xc2x0 C. If it is lower than room temperature, it may become difficult to sufficiently and uniformly hydrolyze the functional end-groups. Therefore, the surface of the functional layer may become uneven in making waterdrops slip down the surface. If it is higher than 70xc2x0 C., hydrolysis and the subsequent polycondensation of the silicone may proceed too much. With this, the number of the reaction sites of the silicone, which are bonded to the substrate or the underlayer may becomes insufficient. Thus, the article may become inferior in making waterdrops slip down the surface thereof. The mixing of the silica precursor sol with the silicone is conducted at a temperature of preferably not higher than 50xc2x0 C., particularly about room temperature. If it is higher than 50xc2x0 C., aggregates may be formed by stirring. With this, the surface of the functional layer may become uneven in making waterdrops slip down the surface.
According to the first aspect of the invention, it is preferable to dry or bake the precursory layer, which has been formed by applying the mixed liquid containing the silicone, acid and water. With this, the functional groups of the functional layer are sufficiently bonded to the substrate or the underlayer. If the drying temperature is too low, the number of the reaction sites of the silicone, which are bonded to the substrate or the underlayer, may become too small. With this, the article may become inferior in making waterdrops slip down the surface thereof. If the drying temperature is higher than 250xc2x0 C., the substances of the mixed liquid may partly alter or decompose by heat. With this, the article also may become inferior in making waterdrops slip down the surface thereof. The drying temperature is particularly preferably from 100 to 150xc2x0 C. in order to further improve the article in making waterdrops slip down the surface thereof.
According to the second and third aspects of the invention, it is preferable to dry or bake the precursory layer, which has been formed by applying the mixed liquid containing the silicone, a silica precursor sol, acid and water, at a temperature of not higher than 250xc2x0 C., more preferably not higher than 150xc2x0 C. With this, the functional groups of the functional layer are sufficiently bonded to the substrate or the underlayer. If the drying temperature is higher than 250xc2x0 C., the substances of the mixed liquid may partly alter or decompose by heat. With this, the article also may become inferior in making waterdrops slip down the surface thereof. If the baking temperature becomes lower, it is necessary to take more time for drying or baking the precursory layer. With this, the functional groups of the functional layer are sufficiently bonded to the substrate or the underlayer. If this drying or baking time is too short, the number of the reaction sites of the silicone and other compounds, which are bonded to the substrate or the underlayer, may become too small. With this, the article may become inferior in making waterdrops slip down the surface thereof.
In the invention, the thickness of the functional layer after its drying is preferably not greater than 100 nm. If it is greater than 100 nm, the functional layer may become inferior in transparency and strength. The article according to the invention is superior in making waterdrops slip down the surface thereof. If, for example, a waterdrop of 5 xcexcL is put on the article, xe2x80x9cthe angle of waterdrop slippagexe2x80x9d may be in a range of 5-30 degrees. The functional layer of the invention can be superior in transparency and thus can be not greater than 4% in haze value defined in Japanese Industrial Standard (JIS) R3212. The inventors unexpectedly found that the article of the invention can be superior to conventional water-repellent articles in making waterdrops slip down the surface thereof, even if the former and the latter are the same with respect to the contact angle of a waterdrop disposed thereon. If this contact angle is too small in the invention, the article may also become inferior in making waterdrops slip down the surface thereof. Therefore, the contact angle of a waterdrop on the article is preferably not less than 70 degrees.